This invention generally relates to a suspension beam for a vehicle, and more particularly to one having a captured axle. The suspension beam, also known as a control arm, and axle assembly of this invention is particularly directed to one wherein the upper and lower beam plates directly engage and retain an axle mounted substantially perpendicular to the beam. Additional structures, such as side plates or rigid webbing would generally be used to increase overall beam stability and rigidity.
The suspension beam assembly of the instant invention has multiple applications but would generally be used for heavy duty trucks and trailers. The beam assembly is adaptable for use with a multitude of hanger types as well as with air ride resilient spring assemblies interposed between the beam and a vehicle chassis. The beam assembly can be used in both overslung and underslung applications, and in certain applications may be mounted in a leading or trailing orientation with respect to its connection to the vehicle chassis.
Generally, the suspension beam will be mounted to a pivot depending from a vehicle chassis. The beam itself extends away from the pivotal attachment a pre-determined length. Any variety of suspension members, such as resilient air bags, coil springs or the like may be mounted between the beam and the vehicle chassis. Further, an axle is generally mounted perpendicular to a pair of spaced apart suspension beams.
It is the attachment of the axle to the beams which is the novel feature of the instant invention. It is highly desirable to have a rigid axle to beam connection which substantially eliminates up and down flexation as well as side to side deflection during suspension articulation. A proper rigid axle-to-beam connection further limits unwanted suspension tracking and suspension deflection as the vehicle encounters uneven surfaces, and as it maneuvers through turns.
Efforts to perfect the axle to beam connection have included positioning the axle between the upper beam member and a separate lower beam member in a clam shell orientation as well as passing the axle directly through the side plates of the beam. A variety of axle sleeves or collars have also been utilized to increase the area of connection between the beam plates and the axle and to enhance the rigidity of the axle-to-beam connection point. Some of the prior art particular to the axle-to-beam connection includes U.S. Pat. No. 5,366,237 to Dilling and U.S. Pat. No. 6,557,875 to Schlosser. Certain prior art suspension beams included cut-out portions into which an axle was positioned and then fastened. Examples of these axle to beam connections can be seen at U.S. Pat. No. 6,827,360 to Chan and U.S. Pat. No. 6,508,482 to Pierce.
An additional problem with typical axle to beam connections in control arm applications is that the forces imparted on the axle may actually stress the cross-sectional shape such that the axle becomes out of round. Numerous forces are imparted on the axle during vehicle operation and including centrifugal force at the vehicle center of gravity which is proportionate to the radius of the curve or corner, as the vehicle maneuvers around a corner, and the vehicle speed squared. This action creates a roll moment proportionate to the height of the center of gravity off the ground and the magnitude of the centrifugal force. Since the vehicle is in a steady state condition, the roll moment is resisted at the tire to road interface by an equal but opposite moment created by unloading the tire of one side of the vehicle by a force and increasing the load on the opposite side tire by the same force magnitude. The roll moment causes the vehicle to lean in one direction which imparts excessive directional force at an axle to beam connection point. Further, tire deflection becomes proportionate to the force magnitude and the radial spring rate of the tires. The forces caused by the roll moment must be transferred from the vehicle body through the suspension into the axles and the tires, and then to the road surface. Transference of the load from the suspension to the axle varies depending on the orientation of the control arm respective its connection to the vehicle.
The forces which are imparted on the axle to beam connection can be changed by altering the method of connecting the axle to the beam. It is desirable to control the application of forces during vehicle maneuvering to eliminate or at least limit excessive forces at any isolated point at the axle to beam connection. A very good description of the overall force application to the axle to beam connection can be found in U.S. Pat. No. 5,366,237 to Dilling. The Dilling patent discloses an axle beam with two spaced apart side plates. A bore is formed completely through the spaced apart side plates in horizontal alignment. The axle is passed through the bore and fixed therein by weldment or other conventional means. As explained in the Dilling patent, this orientation of axle to beam connection allows control of the forces imparted during vehicle maneuvering and limits the application of centrifugal forces as well as side to side deflection. One disadvantage of this orientation is the transference of force between the axle and the beam side plates, specifically along the portion of the side plate disposed between the axle and the upper and lower beam plates. As stated in the Dilling patent, however, the invention achieves its purpose of limiting forces at the axle to beam connection by surrounding the axle with a rigid connection substantially 360 degrees around its circumference. This assertedly prohibits the axle from being stressed out of its manufactured cross-section shape thereby limiting the likelihood of “out of round” from occurring. As stated, this orientation also eliminates the need for additional mechanical fasteners such as U-bolts. As with other prior art configurations, an axle sleeve is sometimes used to further increase rigidity of the connection thereby limiting bending and torquenal forces as the axle to beam connection points.
The instant invention provides an improved suspension beam that further controls the imparting of torsional and bending forces at the axle to beam connection points by eliminating the side plate span between the circumference of the axle and the top and bottom plates of each suspension beam. Each suspension beam includes a first end and a spaced apart second end. At the first end of the suspension beam, a pivotal mount is formed for retaining a resilient bushing which is then inserted into and pivotally attached to a bracket depending from the vehicle chassis. At the second end of the beam, a mount is provided for a resilient air suspension member. It is understood that the mount may be oriented for both overslung and underslung applications.
Between the pivot bushing of the first end and the air bag mount of the second end, a rigid top plate and rigid bottom plate are provided. Intermediate to the ends, an axle is positioned and captured directly between the top plate and bottom plate. It is preferable that the top plate and bottom plate are slightly arced about the periphery of the axle to increase the axle to beam connection span. Because the top plate and bottom plate of the beam are directly connected to the axle, the axis of rotation of the axle lies on the centerline of the beam. Side plates would generally be inserted and fixed between the pivot bushing and the axle as well as between the axle and the second end. This further increases the rigidity and stabilizes the beam. Further, by directly attaching the top plate and bottom plates to the axle, there is no side wall flexing between the axle and those top and bottom plates which would induce stress.
The top and bottom plates both extend from the axle in directions substantially tangent to the axle and are in contact with the surface of the axle along a distance. That distance can be varied by forming a slight arc in the top plate or the bottom plate or both plates. Accordingly, stresses and forces imparted on the axle during vehicle articulation are transferred directly from the axle to the top and bottom plates which then carry those stresses. Further, this orientation directs forces from the axle substantially to the center line of the suspension beam rather than the sidewalls of the beam directly above and below the axle.
This orientation also facilitates ease of manufacture because no holes have to be bored through the beam sidewalls. Positioning an axle through bores in the sidewalls requires a certain degree of tolerance in those bores to facilitate the passage of the axle. Further, tolerance must be provided to allow weldment of the axle to the side plates. This necessity is eliminated by the instant invention.
In another configuration of the invention, the axle is trapped between the top and bottom plates, however, the additional side plates are replaced by a U-shaped member. It is known that the U-shaped member replacing side plates further limits side to side deflection during vehicle articulation.
The orientation of the captured axle with direct connection between the top and bottom plates in the axle surface creates a symmetrical beam. The symmetrical centerline of the axle and beam further allows uniform clearance for disc brakes, actuators, brake camshafts and other accessories.
In some applications it may be desirable and preferable to have an actual sleeve over the axle to eliminate the direct weldment of the top and bottom plates to the axle surface. It is understood, however, the sleeve is optional.
In applications where an axle sleeve is used, the axle sleeve may be flush to the beam sidewalls, or may be mounted inboard or outboard the beam sidewalls. Further, the axle sleeve can be manufactured in one or more pieces and may be provided with windows to enhance weldment of the sleeve to axle or the sleeve to beam.
The sidewalls of the beam may also be replaced by a single center wall which creates a substantial I-beam configuration when the center plate is connected to the top plate and bottom plate of the beam.
In yet another embodiment of the invention, multiple top and bottom plates may be used. The axle may be captured between a first top plate and a first bottom plate. The first top plate then overlies a second top plate while the first bottom plate overlies a second bottom plate. It is further understood the top or bottom plates can be wrapped about the circumference of the axle to increase the surface contact of the axle to the top and bottom plates.